The cited patent applications teach high capacity digital watermarks that can be completely removed, restoring a watermarked content object (e.g., an image) to its original, pristine state. (See also Tian, “Wavelet-Based Reversible Watermarking for Authentication,” Proc. of SPIE, Vol. 4675, pp. 679–690, January, 2002; and Tian, “Reversible Watermarking by Difference Expansion,” Proc. Multimedia Security Workshop, Dec. 6, 2002.)
Other reversible watermnarking techniques are also known, e.g., in Pat. Nos. 5,646,997 and 6,278,791, and in Fridrich et al, “Lossless Data Embedding for All Image Formats,” Proc. SPIE, Vol. 4675, pp. 572–583, January, 2002; Dittmann et al, “Watermarking Protocols For Authentication And Ownership Protection Based On Timestamps And Holograms,” Proc. SPIE, Vol. 4675, pp. 240–251, January, 2002; Fridrich et al, “Invertible Authentication,” Proc. SPIE, Vol. 4314, pp. 197–208, January, 2001; Macq, “Lossless Multiresolution Transform For Image Authenticating Watermarking,” Proceedings of EUSIPCO, Sept. 2000; Vleeschouwer et al, “Circular Interpretation Of Histogram For Reversible Watermarking,” Proceedings of IEEE 4th Workshop on Multimedia Signal Processing, Oct. 2001; Kalker et al, “Capacity bounds And Constructions For Reversible Data Hiding,” Proceedings of the 14th International Conference on Digital Signal Processing, volume 1, pages 71–76, July 2002; and Celik et al, “Reversible Data Hiding,” Proceedings of International Conference on Image Processing, volume II, pages 157–160, Sept. 2002. Other reversible watermarking techniques will doubtless be developed in the future.
The ability to remove a watermark from an encoded image opens the possibility of various novel applications. Several such applications are detailed herein.
One application employs a reversible (frail) watermark in conjunction with a second (robust) watermark. The reversible watermark conveys information that persists so long as the image is not corrupted. After corruption, the information encoded by the reversible watermark is compromised, but information encoded by the robust watermark persists. In this arrangement, the payload of the reversible watermark can convey information about the robust watermark (e.g., encoding parameters, or an error signal), permitting removal of the robust watermark from an uncorrupted encoded image. By such arrangements, the encoded image can be fully restored to its pristine, unencoded state even if several different watermarks have been applied.
In a related application, the information about the robust watermark can be stored in a memory, and accessed through linking data encoded in one of the watermarks.
In all such arrangements, after the watermarks have been removed, an image hash can be computed and checked against a hash made prior to any watermarking, to confirm perfect restoration of the image to its original state. (The latter hash can be conveyed with the image via one of the watermarks, or it can be stored in a memory and accessed through linking data encoded in one of the watermarks.)
A related application builds on the arrangements just-disclosed. When an image is first acquired (or first-entered into an asset management system), it is watermarked with both robust and reversible watermarks. Among other data, the robust watermark conveys an image version number, and a link to a database entry where information about the image is stored.
When a user accesses the image, the watermarks are decoded and their contents are stored locally. The image is then processed to remove the watermarks, and successful image restoration is checked by reference to hash data. Actions taken by the user are appended to an audit log that is maintained as part of the database record for that image. At conclusion of the user's processing, the image is re-watermarked, with the version number updated in the robust watermark.
Still another application also employs a reversible watermark in conjunction with a robust watermark. In this application, however, the reversible watermark conveys metadata associated with the image, whereas the robust watermark conveys a link to a data repository having at least some of the same metadata. By this arrangement, a recipient of an uncorrupted image can decode the watermarked metadata, store this data locally for future reference, and then remove the watermark from the image—enhancing the image quality. If, on the other hand, the image is corrupted prior to its receipt, the inherently-encoded metadata is lost, but can nonetheless be recovered from the store using the linking information provided by the robust watermark. (If desired, the robust watermark may point to a local data repository in which the metadata from the reversible watermark is written after decoding.)
Various combinations of the foregoing and other arrangements are also contemplated.
These and other features and advantages enabled by the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.